Lenses are used for a variety of optical systems, such as camera lenses, light source lenses, etc. In outdoor applications, particularly vehicle-based systems, camera or light source lenses are subject to ambient weather conditions, dirt and debris, and other contaminants which can obstruct or interfere with optical transmission through the lens. It is desirable to provide a substantially clean or clear optical path through the lens for camera-based systems to facilitate proper imaging, and for light source systems to facilitate the expected area illumination. Outdoor surveillance cameras and lighting systems, as well as vehicle-based lighting and camera systems are often inconveniently located for manual cleaning and automated lens cleaning systems are therefore desirable. Ultrasonic cleaning uses an electromechanical transducer, such as a piezoelectric actuator attached to the bottom of a lens element or lens cover plate, to vibrate the lens to remove debris from the lens surface. In some cases, the mechanical system including the transducer and the lens undergoes resonance, and exhibits a particular spatial vibrating pattern as a standing wave determined by its mechanical properties and boundary conditions. However, standing wave excitation of a dirty lens results in a wave front that is fixed in space, and certain portions of the lens called nodal regions do not vibrate. Consequently, cleaning effectiveness is hindered, particularly at or near the nodal regions.